Such a filtering method is described in the ISO document “Proposal of a Generic Bitstream Syntax Description Language” by J. Heuer, A. Hutter, G. Panis, H. Hellwagner, H. Kosch and C. Timmerer (reference ISO/IEC JTC1/SC29/WG11 MPEG02/M8291 Fairfax/May 2002).
In this ISO document, it is proposed to act on a syntactical description of the bitstream rather than on the bitstream itself. A syntactical description is defined as being an XML document describing the high-level structure of the bitstream. The proposed syntactical description comprises elements that are marked with semantically meaningful data. The proposed method consists in defining transformations aimed at removing the elements that are marked with a specific marker from the syntactical description. Then a filtered bitstream is generated from the transformed syntactical description.
An advantage of such a solution is that it generates a filtered bitstream in which the prohibited passages are removed.
This solution uses specific markers and specific transformations associated with said specific markers.
The invention proposes an alternative solution that avoids being limited to predefined markers.